Method of coating ferrous metal with molten aluminum



y 1969 SHIGERU YONEZAKI ETAL 3,457,097

METHOD OF COATING FERROUS METAL WITH MOLTEN ALUMINUM Filed Feb. 5, 1965INVENTORS sweeu YONEZAKI uma oau Md enn l-H ASAKAWA p1. JMMM f PMATTORNEYS United States Patent 3 457,097 METHOD OF COA'IIPiG FERROUSMETAL WITH MOLTEN ALUMINUM Shigeru Yonezaki, Misao Obu, and KenichiAsakawa, Kitakyushu, Japan, assignors to Yawata Iron & Steel Co., Ltd.,Tokyo, Japan, a corporation of Japan Filed Feb. 3, 1965, Ser. No.430,004 Claims priority, application Japan, Feb. 10, 1964, 39/6,793;Mar. 9, 1964, 39/12,924, 39/12,925, 39/ 12,926, 39/ 12,927

Int. Cl. B44d 1/34 US. Cl. 117-51 20 Claims ABSTRACT OF THE DISCLOSUREAn improvement is provided in the method of coating a ferrous metalarticle with aluminum in which the surface of the metal article to becoated is previously reduced by means of reducing gas in a reducing zoneand the article is then introduced into a molten bath of aluminum oralloy thereof while keeping the article out of contact with air. Theimprovement involves the steps of cooling the article after thereduction and pre-treating the surface of the article with a neutral orreducing carrier gas containing vapor of at least 1 of the followingmetals, nonmetals and compounds:

(A) elemental Bi, Sb, P-b, As, Se, P, Mg, Ca, Sr, Ba, Cd;

(B) fluorides of the alkali metals, K, Na, and Li;

(C) M00 K TiF and Na TiF and (D) halides of Si, P, Ti, Zr, V, Nb, Mo,Cr, Ta, W, Mn,

Pb, As, Bi, Sb and Se.

The pretreatment is effected prior to introducing the article into themolten aluminum coating bath.

This invention relates to a method of coating ferrous metal with moltenaluminum, and particularly to an improved method of coating a ferrousmetal article wherein the ferrous metal article to be treated isannealed for surface reduction and then introduced through a protectiveatmosphere into a bath of molten aluminum for coating.

When an aluminum coating is effected in a conventional apparatus asemployed in a hot dip coating process such as the Sendzimir process,there inevitably arise various defects, such as partial absence ofcoating, pinholes, blisters, and deterioration of the thermal resistanceand corrosion resistance of the coated metal article, and it hastherefore been difficult to obtain products of good quality. To overcomethese disadvantages, various improvements and attempts have been madeheretofore. For example, the US Patent No. 3,051,587 disclosed animproved method of making vapor of metallic sodium circulate above thesurface of the coating bath, or interlaying a bath of metal, such asmolten lead, between the protective atmosphere and the molten aluminumbath, in order to avoid various defects that may be produced from thedirect contact of the gas of the protective atmosphere with the moltenaluminum bath.

The object of the present invention is also to provide a method forovercoming the above-mentioned disadvantages, and after numerousstudies, the applicants have found that excellent wettability of steelstrip with coating bath could be obtained by spraying a vapor of ele-"ice ments such as Bi, Sb, Pb, P, As, Se, or compounds such as fluoridesof the alkali metals such as KF, NaF, LiF, oxides or fluorides such asM00 K TiF Na TiF halides of P, Si, Ti, Zr, v, Nb, Ta, Cr, Mo, w, Mn, Pb,As,

Bi, Se, Sb, metals of Group II of the Periodic System' such as Mg, Ca,Sr, Ba, Cd, or the like, onto the surface to be coated of the steelstrip, during the cooling step after the reducing annealing step inaluminum coating by the Sendzimir process, and thus an excellentaluminum coated article having a continuous layer of alloy could beobtained,

The degreased steel strip is introduced into a reducing furnace so thatreducing and annealing processes are conducted simultaneously therein,and after being cooled down to an appropriate temperature in a coolingzone, the strip is dipped in a coating bath. The applicants have foundthat, if the steel strip was first passed through the abovementionedvapor of metals or compound, just before entering the cooling zone ordipping in the coating bath, or was sprayed with vapor, on the surfaceto be coated so that the strip is treated with vapor, and then dipped ina coating bath containing aluminum or aluminum alloy, keeping the stripstrictly out of contact with air, the abovementioned properties couldeasily be incorporated in the coated article.

The significant effects that will be obtained by the embodiment of thepresent invention are that, not only excellent aluminum coated steelstrip that will not produce any defect such as coating gaps, pinholes,and blisters, can be obtained, but also that the coating operation willbe easier and have an excellent operability and productivity.

In the drawings:

FIGURE 1 is a side view of the apparatus showing the aluminum coatingline embodying the present invention.

FIGURE 2 is a side view of the apparatus in FIGURE 1 with vaporgenerating system installed outside the furnace, and

FIGURE 3 is a plan view of the apparatus with vapor spraying nozzleslocated on both sides of the steel strip.

The present invention will now be described in detail, taking forexample the case of aluminum coating of steel strip.

A cold rolled or hot rolled steel strip in the form of coil is unrolledby uncoiler, and oils and other organic substances on the surface of thestrip are removed by oxidizing combustion or cleaned by other suitablemethods. The strip 1 so surface-cleaned, passes through shielded rolls2, enters into reducing annealing furnace 3, and is heated therein to beannealed and subjected to reduction. It then enters into cooling zone 4,and after being cooled down to a certain temperature, it is introducedinto final cooling zone 5, and, passing through hood 6, it is dipped incoating bath 7 Without coming into contact with air. Passing through thecooling zone 4 or at just above the coating bath 7 Within hood 6, thestrip is treated with vapor of such elements as Bi, Sb, Pb, As, Se,fluorides of the alkali metals such as KF, NaF, LiF, oxides or fluoridessuch as M00 K TiF Na TiF halides of P, Si, Ti, Zr, V, Nb, Ta, Cr, Mo,Mn, W, Pb, As, Bi, Se, Sb, metals of Group II of the Periodic Systemsuch as Mg, Ca, Sr, Ba, Cd, sprayed from nozzles 13 onto the surface tobe coated of the strip. Then it is introduced into the coating bath,passes over the pot rolls 8a, 8b, and is withdrawn from the bath.Nozzles 13 for spraying vapor are located at certain intervals on theupperside and underside of the strip (in front and behind the strip whenthe vapor is sprayed within hood 6 in order to uniformly spray vaporonto the surfaces to be coated. When the spraying of vapor from theupperside and underside (or front side and back side) of the stripsubjects the strip to excessively large vibration due to the tension ofthe steel strip within the final cooling zone, the spraying device maybe arranged in such a manner that the spraying of vapor can be effectedfrom both sides of the strip, as shown in FIGURE 3. As for the positionof nozzles 13, it may be slightly different depending on the type ofvapor to be sprayed, but spraying effect is realized as long as a nozzleis located within the extent from cooling zone 4 to the surface of bathwithin hood 6, and better results can be obtained when, if possible, thenozzle is disposed in the cooling zone to effect the spraying of vaportherefrom.

Instead of spraying vapor on to the strip from abovementioned nozzles13, the steel strip may be passed through vapor of the above-mentionedsubstances introduced in the passage of the steel strip 1, so that thesur face of the strip is treated with the vapor.

The vapor is then formed at 11a or 11b, carried by reducing gas, neutralgas, or inert gas injected from 10a or 10b, passed through heatedconduit 12a or 12b into nozzles 13, and then is sprayed therefrom ontothe surface of the steel strip 1. The spraying quantity of vapor isregulated by the flow of the carrier gas and the temperature of thevapor generating system 11a or 11b.

The apparatus shown in FIGURE 1 is one in which the heat of the reducingannealing furnace is utilized as source for generating vapor, andthereby the heating energy of the heating conduit 12a will also beeconomized. Chamber 11a is a vapor-generating system, in which suitablesubstance as above-described is charged and supplemented as it isconsumed.

FIGURE 2 shows an example of the same apparatus with vapor generatingsystem installed outside the furnace; in this case, a heating device isrequired.

It is also necessary to effect heating or heat retaining as required.

The metals or compounds used in this invention are those produced byheating the substances, which are listed below at the accompanyingindustrial vaporizing temperatures indicated by numerals. It is to benoted that the industrial vaporizing temperature referred to hereinmeans the temperature of heating the vapor generating system in order toobtain a quantity of vapor necessary for carrying out the presentinvention.

(A) Elements such as Bi, Sb, Pb, 900 Q; As, Se, 400 C.; Violet P, 250 C.

(B) Fluorides of alkali metals such as K, Na, Li, higher than 900 C.

(C) Oxides or fluorides of alkali compounds such as M 900 C.; K TiF 700C.; Na TiF 900 C.

(D) Halides of nonmetals and metals such as Si, P, Ti, Zr, V, Nb, Mo,Cr, Ta, W, Mn, Pb, As, Sb, Bi, Se.

PCl 60 C. Si Cl 58 C. TiF 150 C. ZrF 600 C. NbF 100 C. TaF 90 C. VF 200C. CrCl 850 C. MoCl 200 C. WCl 270 C. MnCl 700 C. PbF 860 C. SbCl 50 C.BiCl 240 C. SeCl 80 C. AsCl C.

(B) Group H metals such as Mg, 700 C.; Ba, 950 C.; Ca, 900 C.; Cd, 4500.; Sr, 850 C.

The industrial vaporizing temperatures of the various compounds andmetals for generating vapor used in the present invention vary over awide range from lower temperature to higher temperature as listed above,but, in

any case, satisfactory coating state will be obtained when the steelstrip is treated with vapor heated to these vaporizing temperatures at aregion between the cooling zone and the coating bath.

The industrial vaporizing temperatures of the various metals orcompounds used to generate vapor in the present invention are such aslisted above, but, in actual coating process, these temperatures varynaturally according to line speed or width of the strip.

The metals or compounds for generating vapor which are shown separatelyin 5 groups from A to E are, of course, effective when they are usedsolely or in combination of two or more in the same group, but anacceptable result may be expected also when one or more of thesubstances of different groups are used in proper combination by mixing.In such case where more than two of the substances are mixed, vapor canbe generated by the same vapor generating system, but it can also begenerated in separate vapor generating systems and sprayed onto thesurface to be coated of the strip.

Examples carrying out the present invention in molten aluminum coatingwill now be described.

EXAMPLE 1 A coil of cold rolled steel strip of mm. width is coated withaluminum at a speed of 3 m./min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of A.X gas (A.X gas, employed in thepresent example and in the following examples, consists of H 75%, N 25%w./W.). The strip is heated for about 1 minute to 800-950 0, being thusreduced and annealed sufiiciently. Then, it is introduced into thecooling zone, cooled therein in reducing atmosphere down to coating bathtemperature (about 650 C.), and then introduced into the coating bath.At this time, the surface to be coated is treated, immediately beforeentering into coating bath, with vapor of ZrF In this case, thetemperature to generate vapor of ZrF was kept constant at 600 C., and Ngas at 4 liters/min. was used as vapor carrier gas.

The aluminum coated strip thus obtained had continuous layer of alloy,and the coating gaps, pinholes were extremely few, in comparison withstrip untreated.

EXAMPLE 2 A coil of cold rolled steel strip of 90 mm. width is coatedwith aluminum at a speed of 4 m./min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of AX gas. The strip is heated for about 1minute to 800950 C., being thus reduced and annealed sufiiciently. Then,it is introduced into the cooling zone, cooled therein in reducingatmosphere down to coating bath temperature (about 700 C.), and thenintroduced into the coating bath. At this time, the surface to be coatedis treated, immediately before entering into coating bath, with vapor ofK TiF In this case, the temperature to generate vapor of K TiF was keptconstant at 700 C., and N gas at 5 liters/min. was used as vapor carriergas.

The coating of the thus-obtained coated strip is continuous, beingessentially free of coating gaps, and pinholes are extremely few incomparison with untreated strip.

EXAMPLE 3 A coil of cold rolled steel strip having 90 mm. width iscoated with aluminum at a speed of 4 m./min. The strip is previouslycleaned of grease on its surface by burning to achieve oxidation in anoxidizing furnace, and then introduced into a reducing annealingfurnace, the atmosphere of which consists of A.X gas. The strip isheated for about 1 minute to 800-950 0., being thus reduced and annealedsufliciently. Then, it is introduced into the cooling zone, cooledtherein in reducing atmosphere down to coating bath temperature (about650 C.), and then introduced into the coating bath. At this time, thesurface to be coated is treated, being sprayed from both sides in thecentral portion of the hood, with vapor of KF.

In this case, the temperature to generate vapor of KF was kept constantat 950 C., and A.X gas at 5 liters/ min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, beingessentially free of coating gaps, and pinholes are extremely few incomparison with untreated strip.

EXAMPLE 4 A coil of cold rolled steel strip of 90 mm. width is coatedwith aluminum at a speed of 4 tn/min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of A.X gas. The strip is heated for about 1minute to 800950 C., being thus reduced and annealed sufficiently. Then,it is introduced into the cooling zone, cooled therein in reducingatmosphere down to coating bath temperature (about 670 C.), and thenintroduced into the coating bath. At this time, the surface to be coatedis treated, in the final cooling zone, with vapor of Bi.

In this case, the temperature to generate vapor of Bi was kept constantat 930 C., and A.X gas at 4 liters/ min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, beingessentially free of coating gaps, and pinholes are extremely few incomparison with untreated strip.

EXAMPLE 5 A coil of cold rolled steel strip of 90 mm. width is coatedwith aluminum at a speed of 4 m./min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of A.X gas. The strip is heated for about 1minute to 800-950" C., being thus reduced and annealed sufiiciently.Then, it is introduced into the cooling zone, cooled therein in reducingatmosphere down to coating bath temperature (about 650 C.), and thenintroduced into the coating bath. At this time, the surface to be coatedis treated, in the final cooling zone, with vapor of Mg.

In this case, the temperature to generate vapor of Mg was kept constantat 700 C., and A.X gas at 5 liters/ min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, beingessentially free of coating gaps, and pinholes are extremely few incomparison with untreated strip.

EXAMPLE 6 A coil of cold rolled steel strip of 90 mm. width is coatedwith aluminum at a speed of 4 m./min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of A.X gas. The strip is heated for about 1minute to BOO-950 C., being thus reduced and annealed sufficiently.Then, it is introduced into the cooling zone, cooled therein in reducingatmosphere down to coating bath temperature (about 650 C.), and thenintroduced into the coating bath. At this time, the surface to be coatedis treated, in cooling zone, with vapor of Bi and KP.

In this case, the temperature to generate vapor of Bi and KP was keptconstant at 930 C. (Bi; KF 900 C.), and N gas at 5 liters/min.respectively, was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, beingessentially free of coating gaps, and pinholes are extremely few incomparison with untreated strip.

EXAMPLE 7 A coil of cold rolled steel strip of mm. width is coated withaluminum at a speed of 2 m./min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of A.X gas. The strip is heated for about 2minutes to 800950 C., being thus reduced and annealed sufficiently.Then, it is introduced into the cooling zone, cooled therein in reducingatmosphere down to coating bath temperature (about 700 C.), and thenintroduced into the coating bath. At this time, the surface to be coatedis treated, immediately before entering into the coating bath, withvapor of Sb.

In this case, the temperature to generate vapor of Sb was kept constantat 900 C., and N gas at 5 liters/min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous beingessentially free of coating gaps, and pinholes are extremely few incomparison with untreated strip.

EXAMPLE 8 A coil of cold rolled steel strip of mm. width is coated withaluminum at a speed of 3 m./min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of A.X gas. The strip is heated for about 1minute to SOD-950 C., being thus reduced and annealed sufiiciently.Then, it is introduced into the cooling zone, cooled therein in reducingatmosphere down to coating bath temperature (about 660 C.), and thenintroduced into the coating bath. At this time, the surface to be coatedis treated, in the cooling zone, with vapor of NagTiFs.

In this case, the temperature to generate vapor of Na TiF was keptconstant at 900 C., and A.X gas at 6 liters/ min. was used as vaporcarrier gas.

The coating of the thus-obtained coated strip is continuous, beingessentially free of coating gaps, and pinholes are extremely few incomparison with untreated strip.

EXAMPLE 9 A coil of cold rolled steel strip of 90 mm. width is coatedwith aluminum at a speed of 4 m./min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of A.X gas. The strip is heated for about 1minute to 800-950 C., being thus reduced and annealed sufficiently.Then, it is introduced into the cooling zone, cooled therein in reducingatmosphere down to coating bath temperature (about 650 C.), and thenintroduced into the coating bath. At this time, the surface to be coatedis treated, in the hood, with vapor of TiF In this case, the temperatureto generate vapor of TiF was kept constant at C., and N gas at 5liters/min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, beingessentially free of coating gaps, and pinholes are exeremely few incomparison with untreated strip.

EXAMPLE 10 A coil of cold rolled steel strip of 90 mm. width is coatedwith aluminum at a speed of 4 m./min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of A.X. gas. The strip is heated for about1 minute to 800950 C., being thus reduced 7 and annealed sufiiciently.Then, it is introduced into the cooling zone, cooled therein in reducingatmosphere down to coating bath temperature (about 670 C.), and thenintroduced into the coating bath. At this time, the surface to be coatedis treated, immediately before entering into the coating bath, withvapor of NaF.

In this case, the temperature to generate vapor of NaF was kept constantat 930 C., and A.X gas at 6 liters/min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, beingessentially free of coating gaps, and pinholes are extremely few incomparison with untreated strip.

EXAMPLE 11 A coil of cold rolled steel strip of 90 mm. width is coatedwith aluminum at a speed of 4 m./min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of A.X gas. The strip is heated for about 1minute to 800-950 0., being thus reduced and annealed sufficiently.Then, it is introduced into the cooling zone, cooled therein in reducingatmosphere down to coating bath temperature (about 670 C.), and thenintroduced into the coating bath. At this time, the surface to be coatedis treated, in the final cooling zone, with vapor of M In this case, thetemperature to generate vapor of M00 was kept constant at 900 C., and Ngas at 5 liters/min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, beingessentially free of coating gaps, and pinholes are extremely few incomparison with untreated strip.

EXAMPLE 12 A coil of cold rolled steel strip of 90 mm. width is coatedwith aluminum at a speed of 3 m./min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of A.X gas. The strip is heated for about 1minute to BOO-950 0., being thus reduced and annealed sufiiciently.Then, it is introduced into the cooling zone, cooled therein in reducingatmosphere down to coating bath temperature (about 700 C.) and thenintroduced into the coating bath. At this time, the surface to be coatedis treated, in cooling zone, with vapor of CICI In this case, thetemperature to generate vapor of CrCl tinuous, being essentially free ofcoating gaps, and pinholes are extremely few in comparison withuntreated strip.

EXAMPLE 13 A coil of cold rolled steel strip of 90 mm. width is coatedwith aluminum at a speed of 4 m./min. The strip is previously cleaned ofgrease on its surface by burning to achieve oxidation in -an oxidizingfurnace, and then introduced into a reducing annealing furnace, theatmosphere of which consists of A.X gas. The strip is heated for about 1minute to 800-950 C., being thus reduced and annealed sufficiently.Then, it is introduced into the cooling zone, cooled therein in reducingatmosphere down to coating bath temperature (about 670 C.), and thenintroduced into the coating bath. At this time, the surface to be coatedis treated, in the hood, with vapor of Cd.

In this case, the temperature to generate vapor of Cd was kept constantat 460 C., and A.X gas at 4 liters/ min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, beingessentially free of coating gaps, and pinholes are extremely few incomparison with untreated strip.

What is claimed is:

1. In a method of coating a ferrous metal article with aluminum, whereinthe surface of said metal article to be coated is previously reduced bymeans of reducing gas in a reducing zone and said article is thenintroduced into a molten bath of aluminum or alloy thereof while keepingsaid article out of contact with air, the improvement comprising thesteps of cooling said article after said reduction, and pretreating saidsurface with an agent consisting essentially of a neutral or reducingcarrier gas containing vapor of at least one of the following:

(A) elemental Bi, Sb, Pb, As, Se, P, Mg, Ca, Cr, Sr,

Ba, Cd;

(B) fluorides of the alkali metals, K, Na, and Li;

M003, and NazTiFfi; and

(D) halides of Si, P, Ti, Zr, V, Nb, Cr, Ta, Mn, Pb,

As, Bi, Sb and Se,

prior to introducing the thus-treated article into the molten aluminumcoating bath whereby the surface of the ferrous metal article isprovided with a continuous aluminum-containing coating which isessentially free from pinholes and blisters.

2. The improvement according to claim 1, wherein the reduction iseffected concomitantly with annealing, the article is strip ferrousmetal, and the vapor pretreatment is effected by applying the vaporcontaining carrier gas onto the surfaces to be coated, the saidapplication being effected in a final cooling zone following thereducing annealing step.

3. The improvement according to claim 1, wherein the article is stripferrous metal, and the vapor pretreatment is effected by passing saidstrip through vapor containing carrier gas atmosphere providedintermediate (a) a cooling zone into which the strip passes after thereducing annealing step and (b) the surface of the coating bath.

4. The improvement according to claim 1, wherein the reduction iseffected concomitantly with annealing, the article is strip ferrousmetal, and the vapor pretreatment is effected by spraying the vaporcontaining carrier gas as at least one spray onto the surfaces to becoated, the said spraying being effected in a final cooling zonefollowing the reducing annealing step.

5. The improvement according to claim 1, wherein the vapor pretreatmentis effected by spraying the vapor containing carrier gas at an anglefrom both sides of the article.

6. The improvement according to claim 1, wherein the vapor is generatedin a vaporizing zone disposed within the reducing zone and the vapor isentrained by said reducing gas to the point of application thereto tothe surfaces being pretreated.

7. The improvement according to claim 1, wherein the vapor is generatedin a vaporizing zone disposed exteriorly of the reducing zone.

8. The improvement according to claim 2, wherein the vapor is zirconiumtetrafluoride vapor.

9. The improvement according to claim 2, the vapor is potassiumhexafluorotitanate vapor.

10. The improvement according to claim 2, the vapor is potassiumfluoride vapor.

11. The improvement according to claim 2, the vapor is bismuth vapor.

12. The improvement according to claim 2, the vapor is magnesium vapor.

13. The improvement according to claim 2, wherein the vapor is bismuthand potassium fluoride vapor.

14. The improvement according to claim 2, wherein the vapor is antimonyvapor.

15. The improvement according to claim 2, wherein the vapor is sodiumhexafluorotitanate vapor.

16. The improvement according to claim 2, wherein the vapor is titaniumtetrafluoride vapor.

wherein wherein wherein wherein 17. The improvement according to claim2, wherein the vapor is sodium fluoride vapor.

18. The improvement according to claim 2, wherein the vapor ismolybdenum trioxide vapor.

19. The improvement according to claim 2, wherein the vapor is chromiumdichloride vapor.

20. The improvement according to claim 2, wherein the vapor is cadmiumvapor.

References Cited UNITED STATES PATENTS 1,761,850 6/1930 Smith. 2,046,0316 6/ 1936 Rodriguez 1175 1 2,437,919 3/ 1948 Oganowski.

Alferiefi 117-51 Graham. Lundin.

Knapp 11751 Teshi ma et a1. 1 1751 Coburn 11751 Whitfield et a1. Logan11751 Bernick et a1 117-51 ALFRED L. LEAVITT, Primary Examiner U.S. C1.X.R.

